To provide desired amplitude and phase characteristics, antenna reflectors are often shaped, i.e., the surface shape of the antenna is changed from a conic section (a parabola, a paraboloid, ellipse, ellipsoid, hyperbola, or hyperboloid) to a new curvature or shape. This shaping feature is used advantageously in a commonly-owned, co-pending patent application entitled, "Compact Antenna Range Employing Shaped Reflectors", Ser. No. 06/729,338, filed May 1, 1985. The shaping of antenna reflectors is also discussed in an article entitled, "Minimum-Noise Maximum-Gain Telescopes and Realization Method For Shaped Asymmetric Surfaces," by Sebastian Von Hoerner, appearing in the IEEE Transactions on Antennas and Propagation, Volume AP-26, No. 3, May 1978, pages 464 through 471.
Shaped antenna panels, and in fact most antenna panels, are fabricated using a solid bonding fixture shaped to a particular panel shape. Because each panel in an antenna may have a different shape, a solid bonding fixture is needed for each such panel and thus several solid bonding fixtures are required to fabricate an antenna dish. The solid bonding fixture, a machined surface, is essentially a truss structure formed of beam-like members and shaped to produce the final desired panel shape. In a typical assembly operation, a flexible metal panel or skin is securely clamped to the bonding fixture. A honeycomb backup structure is glued to the metal skin and then a second metal panel or skin is glued to the exposed side of the honeycomb structure. Thus a sandwich is formed with honeycomb structure between two flexible sheets of metal. After having been clamped to the bonding fixture for a predetermined curing time, the metal sheets and the honeycomb structure are permanently deformed into the shape defined by the bonding fixture. The fabricated panel is then released from the bonding fixture, attached to a rigid frame, and arranged with other panels to form a complete antenna reflector surface.
Since the bonding fixture is a machined surface, its size and shape must be accurately fixed during a very expensive machining operation. A typical antenna will require five or six differently shaped panels and thus five or six differently shaped bonding fixtures are required. A large part of the antenna cost is devoted to the manufacture of these precision bonding fixtures and often the fixtures are not useable for other antenna reflectors because the shape of the panels depends on the size of the antenna dish and its desired amplitude and phase characteristics. In essence then, the bonding fixtures are custom made for each antenna.
In lieu of the metal-honeycomb-metal sandwich, an antenna panel can be formed by clamping a single metal sheet to the bonding fixture, and gluing a kerfed channel frame to the metal skin. The kerfed frame is a channel member with slits cut into it to make it flexible. After the glue has cured, the assembly is released from the bonding fixture. The skin, which was deformed by the clamps into the proper shape, is now held in that shape by the adhesion to the kerfed channel.
Another technique for fabricating antenna reflectors is disclosed in U.S. Pat. No. 4,021,817 entitled, "Method of Manufacture of Antenna Reflector Having a Predetermined Curve Surface." This patent describes a technique for forming a complete antenna reflector in one step. The reflector is manufactured by grouping a plurality of die members onto a die base and selectively adjusting the height of each die member so that the assembly of die members defines a convex surface conforming to the desired concave surface of the reflector. The perimetrical edges of a metal or synthetic plastic are engaged by a press that forces the metal or plastic under pressure downwardly onto the die members, thereby forming the blank plastic or metal into an antenna reflector having the desired concave surface contour. A disadvantage associated with this invention is that the use of a press allows only concave surface contour reflectors to be made. Further, it is not clear how the adjustable dies are adjusted or how they are locked in place. It appears access to the adjustment and/or locking features must be made from beneath the die base. Lastly, the action of pressing the blank plastic or metal against the die members creates a dimple in the blank at each die member.